The construction drawings are your main basis for defining the required
activities for measuring the quantities of material. Accurate estimating
requires a thorough examination of the drawings. You should carefully read all
notes and references and examine all details and reference drawings. The
orientation of sectional views should be carefully checked. Dimensions shown on
drawings or computed figures shown from those drawings should be used in
preference to those obtained by scaling distances.

You should check the "Revision" section near the title section to ensure that
the indicated changes were made in the drawing itself. You must ensure that the
construction plan, the specifications, and the drawings are discussing the same
project. When there are inconsistencies between general drawings and details,
details should be followed unless they are obviously wrong. When there are
inconsistencies between drawings and specifications, you should follow the
specifications.

As an estimator, you must first study the specifications and then use them
with the drawings when preparing quantity estimates. You should become
thoroughly familiar with all the requirements stated in the specifications. Some
estimators may have to read the specifications more than once to fix these
requirements in their mind. You are encouraged to make notes as you read the
specifications. These notes will be helpful to you later as you examine the
drawings. In the notes, list any unusual or unfamiliar items of work or
materials and reminders for use during examination of the drawings. A list of
activities and materials that are described or mentioned in the specifications
is helpful in checking quantity estimates.

The tables and diagrams in the Seabee Planner's and Estimator's Handbook,
NAVFAC P-405, should save you time in preparing estimates and, when understood
and used properly, provide accurate results. Whenever possible, the tables and
the diagrams used were based on Seabee experience. Where suitable information
was not available, construction experience was adjusted to represent production
under the range of conditions encountered in Seabee construction. A thorough
knowledge of the project drawings and specifications makes you alert to the
various areas where errors may occur.

Accuracy as a Basis for Ordering and Scheduling

Quantity estimates are used as a basis for purchasing materials, determining
equipment, and determining manpower requirements. They are also used in
scheduling progress, which provides the basis for scheduling material
deliveries, equipment, and manpower. Accuracy in preparing quantity estimates is
extremely important; these estimates have widespread uses and errors can be
multiplied many times. Say, for example, a concrete slab is to measure 100 feet
by 800 feet. If you misread the dimension for the 800-foot side as 300 feet, the
computed area of the slab will be 30,000 square feet, when it should actually be
80,000 square feet. Since area is the basis for ordering materials, there will
be shortages. For example, concrete ingredients, lumber, reinforcing materials,
and everything else involved in mixing and placing the concrete, including
equipment time, manpower, and man-hours, will be seriously underestimated and
ordered.

Checking Estimates

The need for accuracy is vital, and quantity estimates should be checked to
eliminate as many errors as possible. One of the best ways to check your
quantity estimate is to have another person make an independent estimate and
then to compare the two. Any differences should be checked to determine which is
right. A less effective way of checking is for another person to take your
quantity estimate and check all measurements, recordings, computations,
extensions, and copy work, keeping in mind the most common error sources (listed
in the next section).

Error Sources

Failure to read all the notes on a drawing or failure to examine reference
drawings results in many omissions. For example, you may overlook a note that
states "symmetrical about the center line" and thus compute only half the
required quantity.

Errors in scaling obviously mean erroneous quantities. Great care should be
taken in scaling drawings so correct measurements are recorded. Common scaling
errors include using the wrong scale, reading the wrong side of a scale, and
failing to note that a detail being scaled is drawn to a scale different from
that of the rest of the drawing. Remember: Some drawings are not drawn to scale.
Since these cannot be scaled for dimensions, you must obtain dimensions from
other sources.

Sometimes wrongly interpreting a section of the specifications causes errors
in the estimate. If there is any doubt concerning the meaning of any part of the
specification, you should request an explanation of that particular part.

Omissions are usually the result of careless examination of the drawings.
Thoroughness in examining drawings and specifications usually eliminates errors
of omission. Checklists should be used to assure that all activities or
materials have been included in the estimate. If drawings are revised after
material takeoff', new issues must be compared with the copy used for takeoff
and appropriate revisions made in the estimate.

Construction materials are subject to waste and loss through handling,
cutting to tit, theft, normal breakage, and storage loss. Failure to make proper
allowance for waste and loss results in erroneous estimates.